This investigation addresses the need to define the neural circuit mechanisms by which the brain processes different types of somesthetic sensory information during actual behavioral situations, especially during active movements of the limbs. As an example of this, the PI has described a phenomenon in which somatic sensory input to the primary somatosensory cortex of the rat is modified according to the phases of reach-to-touch movements of the forelimb. In this, cutaneous sensory inputs from the forepaw projecting to specific classes of cortical neurons are gated-in or gated-out according to whether the stimulation is delivered during the fast movement of the limb toward a target, or during the touch of the target itself. These studies will continue to define the sites in the somatosensory system at which this sensory gating is occurring, in the context of spontaneous or operantly conditioned movements of the forelimb or the whiskers. The possible role that the motor cortex and other biasing sources may play in this phenomenon will also be examined. New techniques for recording multiple single units at multiple levels of the CNS will be employed in these studies.